North Korea has launched several short-range projectiles into the Sea of Japan, the South Korean military has said.
The country's Office of the Joint Chiefs of Staff said it was analysing the objects but declined to say whether they were ballistic missiles.
The ministry said: 'The military is keeping a tight surveillance over the North to cope with further provocations'.
It comes as a US-South Korea joint military exercise is under way.
The Yonhap news agency, however, has claimed they could be missiles.

They landed off the east coast of South Korea's Kangwon province, the military added, after flying 155 miles in a northeasterly direction following a 6.49 am launch.
The news was immediately reported to President Moon Jae-in.

Japan's NHK broadcast said the projectiles did not appear to be objects that could threaten Japan's safety.
The launch is the first by the North since it test-fired a missile on July 28 that could have been designed to reach 6,200 miles, putting parts of the US mainland within reach.
The North tends to test-fire balistic missiles or other projectiles - including those from long-range multiple rocket launchers - in response to US-South Korea joint military exercises.
Tens of thousands of South Korean and US troops are taking part in the 'Ulchi Freedom Guardian' joint military drills, a largely computer-simulated exercise that runs for two weeks in the South.

The Stalinist autocracy of North Korea has conducted two nuclear tests and dozens of missile tests since the beginning of last year, defying world powers and raising fears of a devastating conflict breaking out in East Asia.
On Wednesday, Kim ordered the production of more rocket engines and missile warheads during a visit to a chemical institute of the Academy of Defence Science, an agency that he fostered to develop its ballistic missile programme.

Diagrams and what appeared to be missile parts shown in photographs published in the North's state media suggested Pyongyang was pressing ahead with building a longer-range ballistic missile that could potentially reach any part of the US mainland.
It is also believed to be developing a solid-fuel missile that could be used for submarine launches.
North Korea's state media reported on Saturday that Kim had guided a contest of amphibious landing and aerial strike by its army against targets modelled after South Korean islands near the sea border on the west coast.
Pyongyang later said it had a plan to fire missiles at the US territory of Guam, while President Donald Trump said any threats would be met with 'fire and fury'.

Earlier this week, North Korean state media showed Kim standing next to the diagram of an intercontinental ballistic missile more powerful than any it has previously tested.
The image of the three-stage rocket known as the Hwasong-13 suggested he is fiercely pursuing the creation of a weapon capable of striking anywhere on the US mainland
It followed an escalation in the war of words between the country and US President Donald Trump.
North Korea condemned the military drills the US is conducting with the South and branded Trump 'weird' and 'ego-driven', not long after Trump claimed Kim was starting to 'respect' him.

Kim also threatened to turn the US into 'a heap of ashes' in response to the Ulchi Freedom Guardian drills currently being held in South Korea.
Earlier today, the UN said North Korea had increased its efforts to produce parts for a new nuclear reactor.